Lamp base



FIG. 1 is a reduced scale, perspective view of a lamp base according to my new design, with dashed lines being shown for environmental purposes only;

FIG. 2 is a bottom plan view of the lamp base;

FIG. 3 is a side elevational view thereof, the other side views being identical; and,

FIG. 4 is a top plan view thereof. 

The ornamental design for a lamp base, as shown and described. 